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The alternative sigma factor sigma B and the virulence gene regulator PrfA both regulate transcription of Listeria monocytogenes internalins.

ABSTRACT: Some Listeria monocytogenes internalins are recognized as contributing to invasion of mammalian tissue culture cells. While PrfA is well established as a positive regulator of L. monocytogenes virulence gene expression, the stress-responsive sigma(B) has been recognized only recently as contributing to expression of virulence genes, including some that encode internalins. To measure the relative contributions of PrfA and sigma(B) to internalin gene transcription, we used reverse transcription-PCR to quantify transcript levels for eight internalin genes (inlA, inlB, inlC, inlC2, inlD, inlE, inlF, and inlG) in L. monocytogenes 10403S and in isogenic Delta prfA, Delta sigB, and Delta sigB Delta prfA strains. Strains were grown under defined conditions to produce (i) active PrfA, (ii) active sigma(B) and active PrfA, (iii) inactive PrfA, and (iv) active sigma(B) and inactive PrfA. Under the conditions tested, sigma(B) and PrfA contributed differentially to the expression of the various internalins such that (i) both sigma(B) and PrfA contributed to inlA and inlB transcription, (ii) only PrfA contributed to inlC transcription, (iii) only sigma(B) contributed to inlC2 and inlD transcription, and (iv) neither sigma(B) nor PrfA contributed to inlF and inlG transcription. inlE transcript levels were undetectable. The important role for sigma(B) in regulating expression of L. monocytogenes internalins suggests that exposure of this organism to environmental stress conditions, such as those encountered in the gastrointestinal tract, may activate internalin transcription. Interplay between sigma(B) and PrfA also appears to be critical for regulating transcription of some virulence genes, including inlA, inlB, and prfA.

SUBMITTER: McGann P

PROVIDER: S-EPMC1892873 | biostudies-literature | 2007 May

REPOSITORIES: biostudies-literature

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The alternative sigma factor sigma B and the virulence gene regulator PrfA both regulate transcription of Listeria monocytogenes internalins.

McGann Patrick P Wiedmann Martin M Boor Kathryn J KJ

Applied and environmental microbiology 20070302 9

Some Listeria monocytogenes internalins are recognized as contributing to invasion of mammalian tissue culture cells. While PrfA is well established as a positive regulator of L. monocytogenes virulence gene expression, the stress-responsive sigma(B) has been recognized only recently as contributing to expression of virulence genes, including some that encode internalins. To measure the relative contributions of PrfA and sigma(B) to internalin gene transcription, we used reverse transcription-PC ...[more]

PMID: 17337550

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Project description:Naturally occurring free fatty acids (FFAs) are recognized as potent antimicrobial agents that also affect the production of virulence factors in bacterial pathogens. In the foodborne pathogen Listeria monocytogenes, some medium- and long-chain FFAs act as antimicrobial agents as well as signaling compounds, causing a repression of transcription of virulence genes. We previously observed that the master virulence regulator PrfA is involved in both the antimicrobial and virulence-inhibitory response of L. monocytogenes to selected FFAs, but the underlying mechanisms are presently unknown. Here, we present a systematic analysis of the antimicrobial and PrfA-inhibitory activities of medium- and long-chain FFAs of various carbon chain lengths and degrees of saturation. We observed that exposure to specific antimicrobial and nonantimicrobial FFAs prevented PrfA-dependent activation of virulence gene transcription and reduced the levels of PrfA-regulated virulence factors. Thus, an antimicrobial activity was not compulsory for the PrfA-inhibitory ability of an FFA. In vitro binding experiments revealed that PrfA-inhibitory FFAs were also able to prevent the constitutively active variant PrfA* from binding to the PrfA box in the promoter region of the virulence gene hly, whereas noninhibitory FFAs did not affect its ability to bind DNA. Notably, the unsaturated FFAs inhibited the DNA binding activity of PrfA* most efficiently. Altogether, our findings support a model in which specific FFAs orchestrate a generalized reduction of the virulence potential of L. monocytogenes by directly targeting the key virulence regulator PrfA.IMPORTANCE Listeria monocytogenes is a Gram-positive pathogen able to cause foodborne infections in humans and animals. Key virulence genes in L. monocytogenes are activated by the transcription regulator PrfA, a DNA binding protein belonging to the CRP/FNR family. Various signals from the environment are known to affect the activity of PrfA, either positively or negatively. Recently, we found that specific medium- and long-chain free fatty acids act as antimicrobial agents as well as signaling compounds in L. monocytogenes Here, we show that both antimicrobial and nonantimicrobial free fatty acids inhibit PrfA-dependent activation of virulence gene transcription by interfering with the DNA binding activity of PrfA. Our findings suggest that free fatty acids could be candidates for alternative therapies against L. monocytogenes.

Dataset Information

The alternative sigma factor sigma B and the virulence gene regulator PrfA both regulate transcription of Listeria monocytogenes internalins.

Publications

The alternative sigma factor sigma B and the virulence gene regulator PrfA both regulate transcription of Listeria monocytogenes internalins.

Similar Datasets

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